INSTRUMENTS EMPLOYED IN HEAT 

 INVESTIGATIONS. 



THE various branches of Physics are so closely allied, and each 

 requires for its proper investigation so much assistance from the 

 others, that classification without much repetition is barely possible. 

 But the difficulty is immensely greater when we endeavour to sepa- 

 rate from one another the various subdivisions of one particular 

 branch. We will, therefore, not try to draw any hard and fast 

 lines ; preferring a moderate, and probably useful, amount of repe- 

 tition to the hopeless attempt to obtain a classification in which 

 each head shall be entirely independent of the others. This 

 being clearly understood, we may usefully divide our subject as 

 follows : 



1. Nature of Heat. 



2. Effects of Heat. 



3. Measurement of Heat and Temperature. 



4. Sources of Heat. 



5. Transference of Heat. 



6. Transformations of Heat. 



Of these we may remark, generally, that there is a very close 

 connection between the groups (i), (4), and (6), whose subjects 

 are, in the main, recent additions to our knowledge ; and that 

 (3) depends, at least in all its ordinary practical forms, on some 



